U.S. patent number 9,351,225 [Application Number 14/348,391] was granted by the patent office on 2016-05-24 for method for supporting mobility of user equipment in wireless communication system, and device supporting the same.
This patent grant is currently assigned to LG Electronics Inc.. The grantee listed for this patent is LG ELECTRONICS INC.. Invention is credited to Sung Hoon Jung, Young Dae Lee, Sung Jun Park, Seung June Yi.
United States Patent |
9,351,225 |
Jung , et al. |
May 24, 2016 |
Method for supporting mobility of user equipment in wireless
communication system, and device supporting the same
Abstract
Provided is a method for supporting mobility of a user equipment
in a wireless communication system. The method comprises the
following steps: receiving Mobility State Estimation (MSE) control
information including information for MSE from a network; executing
mobility if a mobility condition is satisfied; updating a mobility
counter on the basis of the MSE control information; estimating a
mobility state of the user equipment on the basis of the updated
mobility counter; and scaling a mobility parameter on the basis of
the estimated mobility state.
Inventors: |
Jung; Sung Hoon (Anyang-si,
KR), Yi; Seung June (Anyang-si, KR), Lee;
Young Dae (Anyang-si, KR), Park; Sung Jun
(Anyang-si, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
N/A |
KR |
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Assignee: |
LG Electronics Inc. (Seoul,
KR)
|
Family
ID: |
48082638 |
Appl.
No.: |
14/348,391 |
Filed: |
October 9, 2012 |
PCT
Filed: |
October 09, 2012 |
PCT No.: |
PCT/KR2012/008154 |
371(c)(1),(2),(4) Date: |
March 28, 2014 |
PCT
Pub. No.: |
WO2013/055071 |
PCT
Pub. Date: |
April 18, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140228032 A1 |
Aug 14, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61545171 |
Oct 9, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
36/32 (20130101); H04W 36/30 (20130101); H04W
8/02 (20130101); H04W 48/20 (20130101); H04W
36/08 (20130101) |
Current International
Class: |
H04W
36/32 (20090101); H04W 8/02 (20090101); H04W
36/30 (20090101); H04W 36/08 (20090101); H04W
48/20 (20090101) |
Field of
Search: |
;455/436,437,439,441,443,44 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1020100050336 |
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May 2010 |
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KR |
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1020110011554 |
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Feb 2011 |
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KR |
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2011123744 |
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Oct 2011 |
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WO |
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Primary Examiner: Taylor; Barry
Attorney, Agent or Firm: Dentons US LLP
Parent Case Text
This application is a 35 USC .sctn.371 National Stage entry of
International Application No. PCT/KR2012/008154, filed on Oct. 9,
2012, and claims priority of U.S. Provisional Application No.
61/545,171 filed Oct. 9, 2011 which are each hereby incorporated by
reference in its entirety.
Claims
What is claimed is:
1. A method for supporting mobility performance of a user equipment
in a wireless communication system, the method comprising:
receiving mobility state estimation (MSE) control information
including information for the MSE from a network; performing
mobility if a condition for the mobility is satisfied; updating a
mobility counter on the basis of the MSE control information;
estimating a mobility state of the user equipment on the basis of
the updated mobility counter; and scaling a mobility parameter on
the basis of the estimated mobility state, wherein the MSE control
information includes a prohibit timer value, which indicates a
counting threshold value to limit the value of the mobility
counter, and duration time in which the counting threshold value is
effective, and wherein the prohibit timer is started with the
prohibit timer value included in the MSE control information.
2. The method of claim 1, wherein updating the mobility counter
includes: checking whether the prohibit timer is terminated;
determining whether to perform the update of the mobility counter
by comparing the mobility counter and the counting threshold value
if the prohibit timer is running; and increasing the mobility
counter by 1, if it is determined that the update of the mobility
counter should be performed.
3. The method of claim 2, wherein determining whether to perform
the update of the mobility counter includes determining to update
the mobility counter, if the value of the mobility counter is less
than the counting threshold value.
4. The method of claim 3, wherein determining whether to perform
the update of the mobility counter includes determining not to
update the mobility counter, if the value of the mobility counter
is equal to or greater than the counting threshold value.
5. The method of claim 1, wherein staring up the prohibit timer
includes: starting the prohibit timer with the prohibit timer value
after the prohibit timer is terminated, if the prohibit timer is
currently running.
6. A wireless device operating in a wireless communication system,
the wireless device comprising: a radio frequency (RF) unit to
transmit or receive a wireless communication signal, and a
processor functionally connected to the RF unit, wherein the
processor is configured to perform the operations of: receiving
mobility station estimation (MSE) control information including
information for the MSE from a network; performing mobility if the
condition for the mobility is satisfied; updating a mobility
counter on the basis of the MSE control information; estimating a
mobility state of the user equipment on the bases of the updated
mobility counter; and scaling a mobility parameter on the basis of
the estimated mobility state, wherein the MSE control information
includes a counting threshold value to limit the value of the
mobility counter and a prohibit timer value to indicate a duration
time in which the counting threshold value is effective, and
wherein the prohibit timer is started with the prohibit timer value
included in the MSE control information.
7. The method of claim 6, wherein updating the mobility counter
includes: checking whether the prohibit timer is terminated;
determining whether to perform the update of the mobility counter
by comparing the mobility counter and the counting threshold value
if the prohibit timer is running; and increasing the mobility
counter by 1, if it is determined that the update of the mobility
counter should be performed.
8. The method of claim 7, wherein determining whether to perform
the update of the mobility counter includes determining to update
the mobility counter, if the value of the mobility counter is less
than the counting threshold value.
9. The method of claim 8, wherein determining whether to perform
the update of the mobility counter includes determining not to
update the mobility counter, if the value of the mobility counter
is equal to or greater than the counting threshold value.
10. The method of claim 6, wherein staring up the prohibit timer
includes: starting the prohibit timer with the prohibit timer value
after the prohibit timer is terminated, if the prohibit timer is
currently running.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wireless communication, and more
particularly, to a method for supporting mobility of a user
equipment in a wireless communication system and to an apparatus
for supporting the same.
2. Background Art
3.sup.rd generation partnership project (3GPP) long term evolution
(LTE) which is improvement of a universal mobile telecommunications
system (UMTS) is introduced as 3GPP release 8. The 3GPP LTE uses
orthogonal frequency division multiple access (OFDMA) in a downlink
and uses single carrier-frequency division multiple access
(SC-FDMA) in an uplink. Multiple input multiple output (MIMO)
having maximum four antennas are adopted. In recent years, 3GPP
LTE-advanced (LTE-A) which is an evolution of the 3GPP LTE has been
discussed.
The microcell, the femto cell, the pico cell, and the like, of
which service area is small may be installed in a specific location
of the macro cell which has wide coverage.
Since the user equipment which is represented as mobile devices
moves, the quality of the mobile service currently provided may be
deteriorated, or the cell that can provide a better service may be
found. In this regards, the user equipment may move into a new cell
and it is referred to mobility performance of the user
equipment.
Since each cell has fixed coverage and the user equipment moves
with a variable speed in a wireless communication system, the
frequency of mobility performance of the user equipment may be
changed. In order to support the mobility of the user equipment in
consideration of the state of movement of the user equipment, the
method of scaling a mobile state estimation (MSE) and mobility
parameter have been supplied.
Meanwhile, due to the characteristics of implementation of a
wireless communication system, the MSE by the user equipment may be
executed without reflecting the actual state of mobility of the
user equipment. That is, since the improper scaling parameter is
applied in the scaling of the mobility parameter, it results in a
phenomenon which the mobility performance of the user equipment is
not properly executed. In order to solve such phenomenon, a method
is required to support more suitably the mobility of the user
equipment by controlling the MSE executed by the user
equipment.
DISCLOSURE
Technical Problem
An object of the present invention is to provide a method for
supporting the mobility of a user equipment in a wireless
communication system and an apparatus for supporting the same.
Technical Solution
In aspect, a method for supporting mobility performance of a user
equipment in a wireless communication system is provided. The
method includes receiving mobility state estimation (MSE) control
information including information for the MSE from a network,
performing mobility if a condition for the mobility is satisfied,
updating a mobility counter on the basis of the MSE control
information, estimating a mobility state of the user equipment on
the bases of the mobility counter updated, and scaling a mobility
parameter on the basis of the mobility state estimated.
The MSE control information may include a prohibit timer value
which indicates a counting threshold value to limit the value of
the mobility counter and duration time in which the counting
threshold value is effective. The method may further include
starting up the prohibit timer which is set up as the prohibit
timer value.
Updating the mobility counter may include checking whether the
prohibit timer is terminated, determining whether the update of the
mobility counter is performed by comparing the mobility counter and
the counting threshold value if the prohibit timer is working, and
increasing the mobility counter by 1, if it is determined to
perform the update of the mobility counter.
Determining whether the update of the mobility counter is performed
may include determining to update the mobility counter, if the
value of the mobility counter is smaller than the counting
threshold value.
Determining whether the update of the mobility counter is performed
may include determining not to update the mobility counter, if the
value of the mobility counter is same or greater than the counting
threshold value.
Staring up the prohibit timer may include starting up the prohibit
timer which is set up as the prohibit timer value after the working
timer is terminated, if the prohibit timer which is set up as the
previous prohibit timer is already in working.
In another aspect, a wireless device operating in a wireless
communication system is provided. The wireless device includes a
radio frequency (RF) unit to transmit or receive a wireless
communication signal, and a processor functionally connected to the
RF unit. The processor is configured to perform of receiving
mobility station estimation (MSE) control information including
information for the MSE from a network, performing mobility if the
condition for the mobility is satisfied, updating a mobility
counter on the basis of the MSE control information, estimating a
mobility state of the user equipment on the bases of the mobility
counter updated, and scaling a mobility parameter on the basis of
the mobility state estimated.
Advantageous Effects
According to an exemplary embodiment of the present invention, more
reinforced MSE may be provided since the MSE control information is
provided to the user equipment. In the heterogeneous network where
the macro cells and other small cells coexist, the improper
mobility counting due to the mobility performance which is not
related to the actual move of the user equipment may be prohibited.
According to an exemplary embodiment of the present invention, in
the wireless communication system in which inter-frequency mobility
is frequently caused, the improper mobility counting due to the
mobility performance which is not related to the actual move of the
user equipment may be prohibited. Through this, the mobility state
of the user equipment which is estimated by the MSE executed by the
user equipment may more suitably reflect the actual mobility of the
user equipment. On the basis of this, the user equipment may
suitably execute mobility according to actual network surroundings
and the state of its mobility.
DESCRIPTION OF DRAWINGS
FIG. 1 illustrates a wireless communication system according to the
present invention.
FIG. 2 is a block diagram illustrating a radio protocol
architecture for a user plane.
FIG. 3 is a block diagram illustrating a radio protocol
architecture for a control plane.
FIG. 4 is a flowchart illustrating an operation of a UE in an RRC
idle state.
FIG. 5 is a flowchart illustrating a process of establishing an RRC
connection.
FIG. 6 is a flowchart illustrating a process of reconfiguring the
RRC connection.
FIG. 7 is a view illustrating an RRC connection re-establishment
procedure.
FIG. 8 is a flowchart illustrating a conventional method of
performing measurement.
FIG. 9 shows an example of a measurement configuration configured
in a user equipment.
FIG. 10 shows an example of deleting a measurement identifier.
FIG. 11 shows an example of deleting a measurement object.
FIG. 12 is a drawing illustrating an example of the HeNB operation
in a wireless communication system.
FIG. 13 is a flow chart illustrating the handover process of the
CSG cell.
FIG. 14 is a drawing illustrating an example of the mobility
performed by the UE in the wireless communication system.
FIG. 15 is a flow chart illustrating the UE how to perform the MSE
according to an embodiment of the present invention.
FIG. 16 is a block diagram that illustrates a wireless apparatus in
which the embodiment of the present invention can be
implemented.
MODE FOR INVENTION
FIG. 1 illustrates a wireless communication system according to the
present invention. The wireless communication system may also be
called an evolved-UMTS terrestrial radio access network (E-UTRAN)
or a long term evolution (LTE)/LTE-A system.
The E-UTRAN includes a base station (BS) 20 that provides a control
plane and a user plane to a user equipment (UE) 10. The UE 10 may
be fixed or movable and may be called other terms such as a mobile
station (MS), a user terminal (UT), a subscriber station (SS), a
mobile terminal (MT), a wireless device, and the like. The base
station 20 represents a fixed station that communicates with the UE
10, and may be called other terms such as an evolved-NodeB (eNB), a
base transceiver system (BTS), an access point, and the like.
The base stations 20 may be connected to each other through an X2
interface. The base station 20 is connected with an evolved packet
core (EPC) 30 through an S1 interface, in more detail, a mobility
management entity (MME) through an S1 MME and a serving gateway
(S-GW) through an SI-U.
The EPC 30 is constituted the MME, the S-GW, and a packet data
network gateway (P-GW). The MME has access information of the UE or
information on a capability of the UE, and the information is
primarily used for mobility management of the UE. The S-GW is a
gateway having the E-UTRAN as an end point and the P-GW is a
gateway having a PDN as the end point.
Layers of a radio interface protocol between the UE and a network
may be divided into an L1 (first layer), an L2 (second layer), and
an L3 (third layer) based three lower layers of an open system
interconnection (OSI) reference model which is widely known in a
communication system and among them, a physical layer that belongs
to the first layer provides an information transfer service using a
physical channel and a radio resource control (RRC) layer
positioned on the third layer serves to control radio resources
between the UE and the network. To this end, the RRC layer
exchanges an RRC message between the UE and the base station.
FIG. 2 is a block diagram illustrating a radio protocol
architecture for a user plane. FIG. 3 is a block diagram
illustrating a radio protocol architecture for a control plane. A
data plane is a protocol stack for user data transmission and the
control plane is a protocol stack for transmitting a control
signal.
Referring to FIGS. 2 and 3, a physical (PHY) layer provides the
information transfer service to an upper layer by using the
physical channel. The physical layer is connected with a medium
access control (MAC) layer as an upper layer through a transport
channel. Data move between the MAC layer and the physical layer
through the transport channel. The transport channel is classified
depending on a transmission method and a transmission feature
through a radio interface.
Data move between different physical layers, that is, between
physical layers of a transmitter and a receiver through the
physical channel. The physical channel may be modulated by
orthogonal frequency division multiplexing (OFDM) and uses a time
and a frequency as the radio resource.
A function of the MAC layer includes mapping between a logic
channel and the transport channel, and multiplexing/demultiplexing
to a transport block provided to the physical channel onto the
transport channel of an MAC service data unit (SDU) that belongs to
the logic channel. The MAC layer provides a service to a radio link
control (RLC) layer through the logic channel.
A function of the RLC layer includes concatenation, segmentation,
and reassembly of an RLC SDU. In order to assure various quality of
services (QoS) requested by a radio bearer (RB), the RLC layer
provides three operating modes of a transparent mode (TM), an
unacknowledged mode (UM), and an acknowledged mode (AM). An AM RLC
provides error correction through an automatic repeat request
(ARQ).
A function of the RLC layer includes concatenation, segmentation,
and reassembly of an RLC SDU. In order to assure various quality of
services (QoS) requested by a radio bearer (RB), the RLC layer
provides three operating modes of a transparent mode (TM), an
unacknowledged mode (UM), and an acknowledged mode (AM). An AM RLC
provides error correction through an automatic repeat request
(ARQ).
The radio resource control (RRC) layer is defined only on the
control plane. The RRC layer serves to control the logic channel,
the transport channel and the physical channels in association with
configuration, re-configuration, and release of radio bearers. The
RB means a logic route provided by the first layer (PHY layer) and
the second layers (the MAC layer, the RLC layer, and the PDCP
layer) in order to transfer data between the UE and the
network.
Setting the RB defines features of the radio protocol layer and
channel in order to provide a specific service and means a process
of setting respective detailed parameters and operating methods.
The RB may be re-divided into two types of a signaling RB (SRB) and
a data RB (DRB). The SRB is used as a passage for transmitting the
RRC message on the control plane and the DRB is used as a passage
for transmitting the user data on the user plane.
When an RRC connection is established between the RRC layer of the
UE and the RRC layer of the E-UTRAN, the UE is in an RRC connected
state and if not, the UE is in an RRC idle state.
A downlink transport channel for transmitting data from the network
to the UE includes a broadcast channel (BCH) for transmitting
system information and besides, the downlink transport channel
includes a downlink shared channel (SCH) for transmitting user
traffic or a control message. Traffic or a control message of a
downlink multicast or broadcast service may be transported through
the downlink SCH or transported through an additional downlink
multicast channel (MCH). Meanwhile, an uplink transport channel for
transporting data from the UE to the network includes a random
access channel (RACH) for transporting an initial control message
and besides, an uplink shared channel (SCH) for transporting the
user traffic or control message.
The logical channel that is positioned on the transport channel and
mapped to the transport channel includes a broadcast control
channel (BCCH), a paging control channel (PCCH), a common control
channel (CCCH), a multicast control channel (MCCH), a multicast
traffic channel (MTCH), and the like.
The physical channel is constituted by a plurality of OFDM symbols
in a time domain and a plurality of sub-carriers in a frequency
domain. One sub-frame is constituted by the plurality of OFDM
symbols in the time domain. A resource block as a resource
allocation unit is constituted by the plurality of OFDM symbols and
the plurality of sub-carriers. Further, each sub-frame may use
specific sub-carriers of specific OFDM symbols (e.g., a first OFDM
symbol) of a corresponding sub-frame for the physical downlink
control channel (PDCCH), that is, an L1/L2 control channel. A
transmission time interval (TTI) is a unit time of transmitting the
sub-frame.
Hereinafter, the RRC state and the RRC connection method of the UE
will be described in detail.
The RRC state represents whether the RRC layer of the UE is
logically connected with the RRC layer of the E-UTRAN and a case in
which both RRC layers are logically connected to each other is
called the RRC connection state and a case in which both RRC layers
are not logically connected to each other is called the RRC idle
state. Since the RRC connection exists in the UE in the RRC
connection state, the E-UTRAN may determine the existence of the
corresponding UE by the unit of a cell to thereby effectively
control the UE. On the contrary, the E-UTRAN may not determine the
UE in the RRC idle state and a core network (CN) is managed by the
unit of a tracking area which a region unit larger than the cell.
That is, it is determined whether the UE in the RRC idle state
exists by the unit of a large region, and the UE needs to move to
the RRC connection state in order to receive a general mobile
communication service such as voice or data.
When a user first turns on a power supply of the UE, the UE first
retrieves an appropriate and thereafter, the UE stays in the RRC
idle state in the corresponding cell. The UE in the RRC idle state
establishes the RRC connection with the E-UTRAN through an RRC
connection procedure at least when the UE in the RRC idle state
needs to make the RRC connection, and is transited to the RRC
connections state. Cases in which the UE in the RRC idle state
needs to make the RRC connection are various, and for example,
uplink data transmission is required due to a user's call attempt
or when a paging message is received from the E-UTRAN, the cases
may include response message transmission thereto.
A non-access stratum layer located above the RRC layer performs
functions such as session management and mobility management.
In order to manage mobility of the UE on the NAS layer, two states
of EPS mobility management (EMM)-REGISTERED and EMM-DEREGISTERED
are defined and both states are applied to the UE and the MME. An
initial UE is in the EMM-DEREGISTERED state and the UE performs a
process of registering the initial UE in a corresponding network
through an initial attach procedure in order to access the network.
When the attach procedure is successfully performed, the UE and the
MME are in the EMM-REGISTERED state.
In order to manage a signaling connection between the UE and the
EPC, two states of an EPS connection management (ECM)-IDLE state
and an ECM-CONNECTED state are defined and both states are applied
to the UE and the MME. When the UE in the ECM-IDLE state makes the
RRC connection with the E-UTRAN, the corresponding UE is in the
ECM-CONNECTED state. When the MME in the ECM-IDLE state makes an S1
connection with the E-UTRAN, the MME is in the ECM-CONNECTED state.
When the UE is in the ECM-IDLE state, the E-UTRAN does not have
context information of the UE. Therefore, the UE in the ECM-IDLE
state performs a UE based mobility associated procedure such as
cell selection or cell reselection without the need for receiving a
command of the network. On the contrary, when the UE is in the
ECM-CONNECTED state, the mobility of the UE is managed by the
command of the network. When the position of the UE in the ECM-IDLE
state is different from a position which the network knows, the UE
notifies a corresponding position of the UE to the network through
a tracking area update procedure.
Next, the system information will be described.
The system information includes required information which the UE
needs to know to access the base station. Therefore, the UE needs
to receive all of the system information before accessing the base
station and further, the UE continuously needs to have latest
system information. In addition, since the system information is
information which all UEs in one cell need to know, the base
station periodically transmits the system information.
According to Phrase 5.2.2 of 3GPP TS 36.331 V8.7.0 (2009-09) "Radio
Resource Control (RRC); Protocol specification (Release 8)", the
system information is divided in to a master information block
(MIB), a scheduling block (SB), and a system information block
(SIB). The MIB allows the UE to know a physical component, for
example, a bandwidth. The SB allows the UE to know transmission
information of the SIBs, for example, a transmission period, and
the like. The SIB is an aggregate of associated system information.
For example, any SIB includes only information on a neighboring
cell and any SIB includes only information on a uplink wireless
channel used by the UE.
In general, a service which the network provides to the UE may be
divided into three types. Further, the UE differently recognizes
even a type of the cell by considering which service the UE
receives. The service type will be first described below and
thereafter, the type of the cell will be described.
1) Limited service: The service may provide an emergency call and
an earthquake and Tsunami warning system (ETWS), and provide the
emergency call and the earthquake and Tsunami warning system (ETWS)
in an acceptable cell.
2) Normal service: The service may mean a public use general
service and may provide the public use general service in a
suitable or normal cell.
3) Operator service: The service may mean a service for a
communication network operator and only the communication network
operator may use the cell and a general user may not use the
cell.
The type of the cell may be divided as below in association with
the service type provided by the cell.
1) Acceptable cell: Cell where the UE may receive the limited
service. The cell is a cell that is not barred in terms of the
corresponding UE and satisfies a cell selection criterion of the
UE.
2) Suitable cell: Cell where the UE may receive the suitable
service. The cell satisfies a condition of the acceptable cell and
simultaneously, satisfies additional conditions. As the additional
conditions, the cell needs to belong to a public land mobile
network (PLMN) which the corresponding UE may access and needs to
be a cell where execution of the tracking area update procedure of
the UE is not barred. When the corresponding cell is the CSG cell,
the corresponding cell needs to be a cell where the UE may access
the cell as a CSG member.
3) Barred cell: The cell is a cell where information indicating
that the corresponding cell is a cell barred through the system
information is broadcasted.
4) Reserved cell: The cell is a cell where information indicating
that the corresponding cell is a cell reserved through the system
information is broadcasted.
FIG. 4 is a flowchart illustrating an operation of a UE in an RRC
idle state. FIG. 4 illustrates a procedure of registering a UE of
which initial power is turned on in the network through a cell
selection process and thereafter, cell reselection is performed as
necessary.
Referring to FIG. 4, the UE selects radio access technology (RAT)
for communicating with the public land mobile network from which
the UE itself intends to receive the service (S410). Information on
the PLMN and the RAT may be selected by a user of the UE and the
information stored in a universal subscriber identity module (USIM)
may be used.
The UE selects a cell having a largest value among cell having
measured larger signal intensity or quality than specific values
(cell selection) (S420). The UE of which power is turned on
performs the cell selection and the execution of the cell selection
may be called initial cell selection. A cell selection procedure
will be described below in detail. After the cell selection, the UE
receives the system information which the base station periodically
sends. The aforementioned specific value represents a value defined
in the system in order to receive an assurance for quality of a
physical signal in transmitting/receiving data. Therefore, the
value may vary depending on the applied RAT.
When network registration is required, the UE performs a network
registration procedure (S430). The UE registers its own information
(e.g., IMSI) in order to receive a service (e.g., paging) n from
the network. The UE does not register the information in the
accessed network whenever selecting the cell, and registers the
information when information (e.g., a tracking area identity (TAI)
of the network that receives from the system information) is
different from information on a network known by the UE).
The UE performs the cell reselection based on a service environment
provided by the cell or an environment of the UE (S440). When a
value of measured intensity or quality of the signal from a base
station from which the UE receives the service is smaller than a
value measured from a base station of a neighboring cell, the UE
selects one of other cells that provide a more excellent signal
feature than the cell of the base station accessed by the UE. This
process is distinguished from the initial cell selection as Process
No. 2 to be cell re-selection. In this case, a temporal constraint
is given in order to prevent the cell from being frequently
reselected with the variation of the signal feature. A cell
selection procedure will be described below in detail.
FIG. 5 is a flowchart illustrating a process of establishing an RRC
connection.
The UE sends to the network an RRC connection request message for
requesting the RRC connection (S510). The network sends an RRC
connection setup message as a response to the RRC connection
request (S520). The UE enters an RRC connection mode after
receiving the RRC connection setup message.
The UE sends to the network an RRC connection setup complete
message used to verify successful completion of establishing the
RRC connection (S530).
FIG. 6 is a flowchart illustrating a process of reconfiguring the
RRC connection. The RRC connection reconfiguration is used to
modify the RRC connection. The RRC connection reconfiguration is
used for perform RB establishment/modification/release, handover,
and measurement setup/modification/release.
The network sends to the UE an RRC connection setup message for
modifying the RRC connection (S610). The UE sends to the network an
RRC connection reconfiguration complete message used to verify
successful completion of establishing the RRC connection
reconfiguration as a response to the RRC connection reconfiguration
(S620).
Next, a procedure in which the UE selects the cell will be
described in detail.
When the power of the UE is turned on or the UE stays in the cell,
the UE performs procedures for receiving the service by
selecting/reselecting a cell having appropriate quality.
The UE in the RRC idle state needs to prepare for receiving the
service through the cell by continuously selecting the cell having
the appropriate quality. For example, the UE of which the power is
just turned on needs to select the cell having the appropriate
quality for registration in the network. When the UE in the RRC
connection state enters the RRC idle state, the UE needs to select
a cell to stay in the RRC idle state. As such, a process in which
the UE selects a cell that satisfies a predetermined condition in
order to stay in a service stand-by state such as the RRC idle
state is referred to as the cell selection. Since the UE performs
the cell selection while the cell in the RRC idle state may not be
decided at present, it is important to select the cell rapidly as
possible. Therefore, in the case of a cell that provides radio
signal quality having a predetermined reference or more, even
though the cell is not a cell that provides the best radio signal
quality for the UE, the cell may be selected in the cell selection
process by the UE.
Hereinafter, a method and a procedure for selecting the cell by the
UE in the 3GPP LTE will be described in detail with reference to
3GPP TS 36.304 V8.5.0 (2009-03) "User Equipment (UE) procedures in
idle mode (Release 8)".
When the power of the UE is turned on at an initial stage, the UE
retrieves the public land mobile network (PLMN) and selects an
appropriate PLMN capable of receiving the service. The PLMN is a
network that is deployed or operated by a mobile network operator.
Each mobile network operator operates one or more PLMNs. The
respective PLMNs may be identified by a mobile country code (MCC)
and a mobile network code (MNC). PLMN information of the cell is
included in the system information and broadcasted. The UE attempts
to register the selected PLMN. When the registration is succeeded,
the selected PLMN becomes a registered PLMN (RPLMN). The network
may signal a PLMN list to the UE and the PLMNs included in the PLMN
list may be considered as the PLMN such as the RPLMN. The UE
registered in the network needs to be reachable by the network.
When the UE is in the ECM-CONNECTED state (similarly, the RRC
connection state), the network recognizes that the UE receives the
service). However, when the UE is in the ECM-IDLE state (similarly,
the RRC idle state), a situation of the UE is not effective in the
eNB, but the situation is stored in the MME. In this case, the
position of the UE which is in the ECM-IDLE state is known to only
the MME as granularity of a list of tracking areas (TAs). A single
TA is identified by a tracking area identity configured by the PLMN
identity to which the TA belongs and the tracking area code (TAC)
uniquely expressing the TA in the PLMN.
Subsequently, the UE selects a cell having signal quality and
feature to receive an appropriate service among cells provided by
the selected PLMN.
The cell selection process is generally divided into two types.
First, as an initial cell selection process, the UE has no advance
information on the radio channel during this process. Therefore,
the UE retrieves all radio channels in order to find the
appropriate cell. The UE finds the strongest cell in each channel.
Thereafter, the UE selects the corresponding cell only at the time
of finding the suitable cell that satisfies the cell selection
criterion.
Next, the UE may select the cell by using stored information or
using information broadcasted in the cell. Therefore, the cell
selection may be rapidly performed as compared with the initial
cell selection process. When the UE only finds the cell that
satisfies the cell selection criterion, the UE selects the
corresponding cell. When the UE does not find the suitable cell
that satisfies the cell selection criterion through such a process,
the UE performs the initial cell selection process.
After the UE selects a predetermined cell through the cell
selection process, the strength or quality of the signal between
the UE and the base station may be changed due to the mobility of
the UE or a change of a wireless environment. Therefore, when the
quality of the selected cell deteriorates, the UE may select
another that provides higher quality. When the cell is again
selected as such, a cell that provides higher signal quality than
the currently selected cell is generally selected. The process is
referred to as the cell reselection. The cell reselection process
generally has a basic object o select the cell having the highest
quality to the UE.
In addition to the quality of the radio signal, the network decides
a priority for each frequency to notify the priority to the UE. The
UE that receives the priority preferentially considers the priority
to a radio signal quality criterion during the cell reselection
process.
There may be a method for selecting or reselecting the cell
according to the signal feature of the wireless environment and
there may be a cell reselection method described below according to
the features of the RAT and the frequency of the cell.
Intra-frequency cell reselection: The UE reselect a cell having the
same RAT and the same center-frequency as a cell which is being
camping. Inter-frequency cell reselection: The UE reselects a cell
having the same RAT and a different center-frequency as the cell
which is being camping. Inter-RAT cell reselection: The UE reselect
a cell using an RAT different from an RAT which is being
camping.
A principle of the cell reselection process will be described
below.
First, the UE measures the qualities of the serving cell and the
neighboring cell for the cell reselection.
Second, the reselection is performed based on the cell reselection
criterion. The cell reselection criterion has features described
below in association with the measurement of the serving cell and
the neighboring cell.
The intra-frequency cell reselection is basically based on ranking.
The ranking defines an index value for evaluating the cell
reselection and the cells are ordered in the order of the index
value by using the index value. A cell having the best index is
generally called a best ranked cell. The cell index value is based
on a value which the UE measures for the corresponding cell and is
applied with a frequency offset or a cell offset as necessary.
The inter-frequency cell reselection is based on a frequency
priority provided by the network. The UE attempts to camp on a
frequency having the highest frequency priority. The network may
provide the frequency priority to which in-cell UEs will commonly
apply through broadcast signaling or provide a frequency-dedicated
priority for each UE through UE-dedicated signaling.
The network may provide a parameter (e.g., a frequency-specific
offset) used for the cell reselection to the UE for the
inter-frequency cell reselection for each frequency.
The network may provide a neighboring cell list (NCL) used for the
cell reselection to the UE for the intra-frequency cell reselection
or the inter-frequency cell reselection. The NCL includes a
cell-specific parameter (e.g., cell-specific offset) used in the
cell reselection.
The network may provide a cell reselection black list used for the
cell reselection to the UE for the intra-frequency cell reselection
or the inter-frequency cell reselection. The UE does not perform
the cell reselection for a cell included in the black list.
Subsequently, the ranking performed during the cell reselection
evaluating process will be described.
A ranking criterion used to give the priority of the cell is
defined as illustrated in Equation 1.
R.sub.S=Q.sub.meas,s+Q.sub.hyst, R.sub.n=Q.sub.meas,n-Q.sub.offset
[Equation 1]
Herein, Rs represents a ranking criterion of the serving cell, Rn
represents a ranking criterion of the neighboring cell, Qmeas,s
represents a quality value which the UE measures for the serving
cell, Qmeas,n represents a quality value which the UE measures for
a neighboring cell, Qhyst represents a hysteresis value for the
ranking, and Qoffset represents an offset between two cells.
In an intra-frequency, when the UE receives an offset Qoffsets,n
between the serving cell and the neighboring cell,
Qffoset=Qoffsets,n and when the UE does not receive Qoffsets,n,
Qoffset=0.
In an inter-frequency, when the UE receives the offset Qoffsets,n
fir the corresponding cell, Qoffset=Qoffsets,n+Qfrequency and when
the UE does not receive Qoffsets,n, Qoffset=Qfrequency.
When the ranking varies while the ranking criterion Rs of the
serving cell and the ranking criterion of the neighboring cell Rn
are similar to each other, the ranking is frequently reversed, and
as a result, the UE may alternatively reselect both cells. Qhyst
represents a parameter for preventing the UE from alternatively
reselecting both cells by giving hysteresis in cell
reselection.
The UE measures the Rs of the serving cell and the Rn of the
neighboring cell according to the above equation and regards a cell
having the largest ranking criterion value as the best ranked cell
and reselects this cell.
According to the criterion, it can be seen that the quality of the
cell acts as the most important criterion in the cell reselection.
If the reselected cell is not the suitable cell, the UE excludes
the corresponding frequency or the corresponding cell from a cell
reselection target.
Hereinafter, Radio Link Monitoring (RLM) is described.
A user equipment monitors downlink quality based on a cell-specific
reference signal for sensing downlink radio link quality of a
PCell. The user equipment estimates downlink radio link quality for
the purpose of monitoring the downlink radio link quality of the
PCell and compares the estimated result with thresholds Qout and
Qin. The threshold Qout is defined as a level where a downlink
radio link cannot be received stably, and this corresponds to a 10%
error block error rate of hypothetical PDCCH transmission taking
into account a PDFICH error. The threshold Qin is defined as a
downlink radio link quality level at which reception may be made
more stable than at the Qout level, and this corresponds to a 2%
block error rate of hypothetical PDCCH transmission considering a
PCFICH error.
A radio link failure is now described.
A user equipment continues to perform measurement in order to
maintain quality of a radio link with a serving cell receiving a
service. The user equipment determines whether communication is
impossible under current circumstance due to a quality
deterioration of a radio link with the serving cell. If the quality
of the serving cell is too low and thus communication is nearly
impossible, the user equipment determines the current circumstance
as being at a radio link failure.
If it is determined a radio link failure, the user equipment
abandons communication with the current serving cell and chooses a
new cell through a cell selection (or cell reselection) procedure,
then attempting to do RRC connection re-establishment to the new
cell.
3GPP LTE standards provide the following as examples of normal
communication being impossible: When determined that the user
equipment has a serious problem with the downlink communication
link quality based on a radio quality measurement result of the
user equipment's physical layer (when determined that PCell's
quality is low while performing RLM) When determined that there is
a problem with uplink transmission due to continuous failures in
random access procedure in the MAC sublayer. When determined that
there is a problem with uplink transmission due to continuous
failures in uplink data transmission in RLC sublayer. When
determined that handover has failed. When the message received by
the user equipment fails to pass integrity test.
Hereinafter, an RRC connection re-establishment procedure is
described in greater detail.
FIG. 7 is a view illustrating an RRC connection re-establishment
procedure.
Referring to FIG. 7, a user equipment stops using all configured
radio bearers except SRB 0 (Signaling Radio Bearer #0) and
initializes various sublayers of the Access Stratum (AS) (S710).
Further, the user equipment sets each sublayers and physical layer
as default configurations. During this course, the user equipment
maintains an RRC connected state.
The user equipment performs a cell selection procedure for
fulfilling an RRC connection re-establishment procedure (S720). The
cell selection procedure of the RRC connection re-establishment
procedure may be carried out like the cell selection procedure that
is performed by the user equipment in an RRC idle state.
The user equipment determines whether a corresponding cell is a
proper cell by checking system information of a corresponding cell
after performing the cell selection procedure (S730). In case the
selected cell is determined to be a proper E-UTRAN cell, the user
equipment sends an RRC connection re-establishment request message
to a corresponding cell (S740).
Meanwhile, in case it is determined that the cell selected through
a cell selection procedure for performing an RRC connection
re-establishment procedure is a cell using other RAT than E-UTRAN,
the RRC connection re-establishment procedure is stopped and the
user equipment enters into the RRC idle state (S750).
The user equipment may be implemented to finish identifying a
cell's properness within a limited time by a cell selection
procedure and receiving system information of the selected cell.
For this, the user equipment may drive a timer as it initiates the
RRC connection re-establishment procedure. The timer may be paused
in case the user equipment is determined to have selected a proper
cell. In case the timer expires, the user equipment deems the RRC
connection re-establishment procedure as failing and may enter into
the RRC idle state. This timer, hereinafter, is referred to as a
radio link failure timer. In LTE standards TS 36.331, a timer named
T311 may be put to use as the radio link failure timer. The user
equipment may acquire the timer's set value from the system
information of the serving cell.
When receiving the RRC connection re-establishment request message
from the user equipment and accepting the request, the cell sends
out an RRC connection re-establishment message.
When receiving the RRC connection re-establishment message from the
cell, the user equipment reconfigures an RLC sublayer and a PDCP
sublayer on SRB1. Further, the user equipment re-calculates various
key values related to security setting and reconfigures a PDCP
sublayer in charge of security with the newly calculated security
key values. By doing so, SRB1 between the user equipment and the
cell is opened and an RRC control message may be exchanged. The
user equipment completes resuming SRB1 and sends an RRC connection
re-establishment complete message indicating the RRC connection
re-establishment procedure to the cell (S760).
In contrast, when receiving the RRC connection re-establishment
request message from the user equipment and not accepting the
request, the cell sends to the user equipment an RRC connection
re-establishment reject message.
If the RRC connection re-establishment procedure is successfully
performed, the cell and the user equipment conduct an RRC
connection re-establishment reconfiguration procedure. Accordingly,
the user equipment turns back to the state before performing the
RRC connection re-establishment procedure and maximally guarantees
service continuity.
The user equipment, if an RLF or handover failure occurs, reports
such failure event to the network in order to support the network's
Mobility Robustness Optimization (MRO).
When reestablishing RRC connection, the user equipment may offer an
RLF report to an eNB. Radio measurement included in the RLF report
may be used as potential cause of failure so as to identify
coverage issues. This information may be used in MRO evaluation for
intra-LTE mobility connection failure, in order to exclude such
events and put other events to use as inputs for other
algorithms.
In case RRC connection re-establishment fails or the user equipment
fails to perform RRC connection re-establishment, the user
equipment may make reconnection in the idle mode and then generate
a valid RLF report for the eNB. For such purpose, the user
equipment may store information regarding the latest RLF or
handover failure, and until the RLF report is brought up by the
network or for 48 hours after the RLF or handover failure is
sensed, may inform the LTE cell that RLF report is valid at every
subsequent RRC connection (re)establishment and handover.
The user equipment maintains the information while it undergoes a
state shift and RAT varies, and after back to the LTE RAT,
indicates again that RLF report is valid.
The RLF report being valid in the RRC connection configuration
procedure is to indicate that the user equipment is interfered,
like going through connection failure, and due to such failure, the
RLF report is not yet delivered to the network. The RLF report from
the user equipment contains the following information: Last cell
that has offered service to the user equipment (in case of RLF) or
target's E-CGI in handover. Unless E-CGI has been known, PCI and
frequency information are used instead. E-CGI of the cell where
reestablishment has been attempted. E-CGI of the cell that provided
service to the user equipment upon initialization of the last
handover, as an example, when message 7 (RRC connection
reconfiguration) was received by the user equipment. Elapsed time
from last handover initialization to connection failure.
information indicating whether connection failure is attributed to
RLF or handover failure. Radio measurements. failure's
position.
When receiving the RLF failure from the user equipment, the eNB may
forward the report to the eNB that provided service to the user
equipment before the reported connection failure.
In a mobile communication system, it is inevitable for a user
equipment to support mobility. Accordingly, the user equipment
continuously measures quality for a serving cell currently
providing service and quality for a neighbor cell. The user
equipment reports a measurement result to the network at a proper
time, and the network provides the optimal mobility to the user
equipment through, e.g., handover. The measurement for such purpose
is often referred to as Radio Resource Management (RRM)
measurement.
The user equipment, in order to provide information helping a
service provider to operate a network in addition to the purpose of
supporting mobility, may perform measurement for a specific purpose
configured by the network and report a measurement result to the
network. For example, the user equipment receives broadcast
information of a specific cell determined by the network. The user
equipment may report the serving cell with a cell identifier of the
specific cell (this is also referred to as a global cell
identifier), information for identifying the location where the
specific cell belongs (for example, Tracking Area Code), and/or
other cell information (for example, whether a Closed Subscriber
Group (CSG) cell is a member).
When the user equipment, which is on the move, identifies that
quality of a specific area is very bad through measurement, the
user equipment may report the location information on the
band-quality cells and measurement result to the network. The
network may achieve its optimization based on the measurement
result reports from the user equipments helping operating the
network.
In a mobile communication system having a frequency reuse factor of
1, mobility may be mostly attained between different cells that
belong to the same frequency band. Accordingly, in order to insure
the user equipment's mobility well, the user equipment should be
able to measure well cell information and quality of neighbor cells
having the same center frequency as the serving cell. As such,
measurement on the cell having the same center frequency as the
center frequency of the serving cell is referred to as
intra-frequency measurement. The user equipment conducts
intra-frequency measurement and reports the measurement result to
the network at a proper time, so that the goal corresponding to the
measurement result can be achieved.
A mobile service provider may operate a network using a plurality
of frequency bands. In case a communication system service is
offered through a plurality of frequency bands, the user equipment,
in order for the optimal mobility to be provided to the user
equipment, should be able to measure well cell information and
quality of neighbor cells having different center frequencies than
the center frequency of the serving cell. As such, measurement on
the cell having a different center frequency than the center
frequency of the serving cell is referred to as inter-frequency
measurement. The user equipment should be able to conduct
inter-frequency measurement and report the measurement result to
the network at a proper time.
In case the user equipment supports measurement on a heterogeneous
network, measurement on a cell in the heterogeneous network may be
conducted by the base station configuration. Such measurement on
the heterogeneous network is referred to as inter-Radio Access
Technology (RAT) measurement. For example, the RAT may include GSM
EDGE Radio Access Network (GERAN) and UMTS Terrestrial Radio Access
Network (UTRAN) observing the 3GPP standards, as well as CDMA 2000
systems that follow the 3GPP2 standards.
FIG. 8 is a flowchart illustrating a conventional method of
performing measurement.
The user equipment receives measurement configuration information
from the base station (S810). A message containing the measurement
configuration information is referred to as a measurement
configuration message. The user equipment conducts measurement
based on the measurement configuration information (S820). The user
equipment reports a measurement result to the base station if the
measurement result meets a reporting condition in the measurement
configuration information (S830). A message containing the
measurement result is referred to as a measurement report
message.
The measurement configuration information may contain the following
information:
(1) measurement object information: information regarding an object
on which the user equipment is to conduct measurement. The
measurement object includes at least any one of an intra-frequency
measurement object that is an intra-cell measurement object, an
inter-frequency measurement object that is an inter-cell
measurement object, and an inter-RAT measurement object that is an
object of inter-RAT measurement. For example, the intra-frequency
measurement object may indicate a neighbor cell having the same
frequency band as the serving cell, the inter-frequency measurement
object may indicate a neighbor cell having a different frequency
band from the serving cell, and the inter-RAT measurement object
may indicate a neighbor cell of a different RAT from a RAT of the
serving cell.
(2) Reporting configuration information: information on the
reporting condition and type as to when the user equipment reports
a measurement result. The reporting condition may contain
information regarding a period or event triggering a measurement
result report. The reporting type is information as to what type a
measurement result is configured in.
(3) measurement identifier information: information on a
measurement identifier linking a measurement object with a
reporting configuration to thereby determine in what type the user
equipment is to report on what measurement object. Each measurement
identifier links a measurement object to a reporting configuration.
By configuring multiple measurement identifiers, it is available
that more than one measurement object is linked to the identical
reporting configuration as well as more than one reporting
configuration is linked to the identical measurement object. The
measurement identifier may be used as a reference number in the
measurement report. The measurement identifier information is
included in a measurement reporting message and represents which
measurement object is in relation to the measurement result, and
which reporting condition is used to output the measurement
report.
(4) Quantity configuration information: The quantity configuration
information defines the quantity of measurement and relevant
filtering used for the evaluation of the all events and reporting
involved in the measurement type. One filter may be configured per
measurement quantity.
(5) Measurement gap information: This is information for the
measurement gap which is an interval that can be used only for
measuring without consideration of the data transmission between a
UE and the serving cell, which is caused that the downlink
transmission or the uplink transmission is not scheduled.
The user equipment has a measurement object list, a reporting
configuration list and a measurement identifier list to perform a
measurement procedure.
In 3GPP LTE, a base station may configure for a user equipment only
one measurement object per frequency band. According to 3GPP TS
36.331 V8.5.0 (2009-03) "Evolved Universal Terrestrial Radio Access
(E-UTRA) Radio Resource Control (RRC); Protocol specification
(Release 8)" Ch. 5.5.4, events triggering a measurement report are
defined as shown in the following table.
TABLE-US-00001 TABLE 1 Event Reporting Condition Event A1 Serving
becomes better than threshold Event A2 Serving becomes worse than
threshold Event A3 Neighbor becomes offset better than serving
Event A4 Neighbor becomes better than threshold Event A5 Serving
becomes worse than threshold1 and neighbor becomes better than
threshold2 Event B1 Inter RAT neighbor becomes better than
threshold Event B2 Serving becomes worse than threshold1 and inter
RAT neighbor becomes better than threshold2
If the user equipment's measurement result meets a configured
event, the user equipment sends a measurement report message to the
base station.
FIG. 9 shows an example of a measurement configuration configured
in a user equipment.
First, measurement identifier 1 links an intra-frequency
measurement object with reporting configuration 1 901. The user
equipment conducts intra-frequency measurement and uses reporting
configuration 1 for determining a reference of a measurement result
report and reporting type.
Measurement identifier 2 902, like measurement identifier 1, is
linked with an intra-frequency measurement object, but links the
intra-frequency measurement object with reporting configuration 2.
The user equipment conducts measurement and uses reporting
configuration 2 for determining a reference of measurement result
report and reporting type.
By measurement identifier 1 901 and measurement identifier 2 902,
the user equipment sends a measurement result on the
intra-frequency measurement object as long as the measurement
result satisfies either reporting configuration 1 and reporting
configuration 2.
Measurement identifier 3 903 links inter-frequency measurement
object 1 with reporting configuration 3. The user equipment reports
a measurement result on inter-frequency measurement object 1 if the
measurement result meets a reporting condition contained in
reporting configuration 1.
Measurement identifier 4 904 links inter-frequency measurement
object 2 with reporting configuration 2. The user equipment reports
a measurement result on inter-frequency measurement object 2 when
the measurement result meets a reporting condition included in
reporting configuration 2.
Meanwhile, measurement objects, reporting configurations, and/or
measurement identifiers may be added, changed, and/or deleted. This
may be indicated by the base station sending a new measurement
configuration message or measurement configuration changing message
to the user equipment.
FIG. 10 shows an example of deleting a measurement identifier. If
measurement identifier 2 902 is deleted, measurement on the
measurement object associated with measurement identifier 2 902 is
stopped, and no measurement report is sent out. The measurement
object or reporting configuration associated with the deleted
measurement identifier might not be changed.
FIG. 11 shows an example of deleting a measurement object. If
inter-frequency measurement object 1 is deleted, the user equipment
deletes measurement identifier 3 903 associated thereto, as well.
Measurement on inter-frequency measurement object 1 is stopped and
no measurement report is sent out. However, the reporting
configuration associated with the deleted inter-frequency
measurement object 1 might not be varied or deleted.
If a reporting configuration is removed, the user equipment leaves
out a measurement identifier associated thereto, as well. The user
equipment pauses measurement on the measurement object associated
by the associated measurement identifier. However, the measurement
object associated with the deleted reporting configuration might
not be varied or deleted.
The measurement report may contain a measurement identifier,
measured quality of the serving cell, and a measurement result of a
neighbor cell. The measurement identifier identifies a measurement
object for which a measurement report has been triggered. The
measurement result of the neighbor cell may contain the neighbor
cell's cell identifier and measured quality. The measured quality
may contain at least one of Reference Signal Received Power (RSRP)
and Reference Signal Received Quality (RSRQ).
Hereinafter, accessibility measurement is described.
There are many aspects as to coping with non-availability
measurement of connection for a user equipment, and this treats all
of common channels and connection procedures. To inform a network
of non-availability of connection and accordingly help parameter
optimization for increasing connection availability, the user
equipment conducts accessibility measurement upon failure of
connection establishment. In order for accessibility measurement,
the user equipment performs the following logging: A time stamp
generated by using a relative timer counting the time between
failure and reporting is included. The saving time for
accessibility measurement is 48 hours. Reporting the number of
random access preambles transmitted is supported. Indicating
whether to reach the maximum power level is included. Indicating
whether contention is sensed during a random access procedure for
connection establishment is included.
H(e)NB will now be described.
The mobile communication service may be provided by a person, a
specific service provider or a base station that belongs to a group
as well as a mobile network service provider. Such a base station
is referred to a Home NB (HNB) or a Home eNB (HeNB). Hereinafter,
as a general term of the both HNB and HeNB, HeNB will be used. The
object of the HeNB is basically to provide the specific service
which is available only for the closed subscriber group (CSG). But
it may provide service to different users as well as the CSG
according to the operation mode configuration of the HeNB.
FIG. 12 is a drawing illustrating an example of the HeNB operation
in a wireless communication system.
Referring to FIG. 12, a Home eNB gateway (HeNB GW) may be operated
to provide service of the above mentioned HeNB. The HeNB is
connected to the EPC via the HeNB GW or to the EPC directly. The
HeNB GW looks like a general eNB to the MME. Accordingly, the HeNB
and the HeNB GW are connected via S1 interface, and the HeNB GW and
the EPC are also connected via S1 interface. In addition, in case
that the HeNB and the EPC are directly connected, they are
connected via S1 interface. The function of the HeNB is mostly the
same as that of general eNB.
Generally, the HeNB has a lower wireless transmission output
compared to the eNB owned by the mobile network service provider.
Accordingly, it is normal that the service coverage provided by the
HeNB is smaller than the service coverage provided by the eNB. Due
to the characteristics as such, in the aspect of the service area,
the cell provided by the HeNB is sometimes classified by a femto
cell in comparison with the macro cell provided by the eNB.
Meanwhile, in the aspect of the service provided, if the HeNB
provides service only for the CSG group, the cell provided by the
HeNB is referred to the CSG cell.
Each CSG cell has its own identification number, and the
identification number is called the CSG identity (ID). A UE may
have the list of the CSG to which it belongs as a member, and the
CSG list may be changed by the request of the UE or the command of
network. Normally, one HeNB may support one CSG.
By transferring CSG ID of the CSG supported by the HeNB via the
system information, the HeNB may let only member UEs of the
relevant CGS access. When a UE finds the CSG cell, the UE may check
which CSG is supported by the CSG cell by reading the CSG ID
included in the system information. The UE that reads the CSG ID
regards the cell as an accessible cell only in case that the UE
itself is a member of the corresponding CSG cell.
It is not necessary that the HeNB always permits an access only to
the CSG UE. According to the component configuration of the HeNB,
an access of the UE which is not the CSG member may be permitted.
Which UE is permitted to access is changed according to the
component configuration of the HeNB, and the component
configuration means the configuration of operational mode of the
HeNB. The operational modes of the HeNB are classified into three
modes according to which UE the service is provided for. Closed
access mode: A mode that provides service only to specific CSG
members. The HeNB provides the CSG cell. Open access mode: A mode
that provides service for all without any limitation of the
specific CSG member like the general eNB. The HeNB provides the
general cell, not the CSG cell. Hybrid access mode: A mode that may
provides the CSG service to the specific CSG member, and provides
service to the non-CSG member like the general cell. It is
recognized by the CSG member UE as the CSG cell, and recognized by
the non-CSG member UE as the general cell. Such cell is called the
hybrid cell.
By notifying the UE whether the cell to which the HeNB itself
offers service is the general cell or the CGS cell, the HeNB let
the UE detect whether they can access the corresponding cell or
not. The HeNB which is operated in the closed access mode
broadcasts that its own self is the CSG cell via the system
information. The HeNB which is operated in the open access mode
broadcasts that its own self is not the CSG cell via the system
information. As such, the HeNB includes the CSG indicator of 1 bit
in the system information which notifies whether the cell to which
the HeNB itself. For example, the CSG cell broadcasts with the CSG
indicator set to be TRUE. If the cell to which it offer service is
not the CSG cell, a method may be used, either which the CSG
indicator is set to be FALSE or which the transmission of the CSG
indicator is omitted. Since a UE must distinguish the general cell
which is provided by the eNB from the CSG cell, the general eNB
also transmits the CSG indicator and may also let the UE know that
the cell type provided by its own self is the general cell. The
general eNB may let the UE know that the cell type provided by its
own self is the general cell not by transmitting the CSG indicator.
Table 2 represents the parameter relevant to the CSG which is
transmitted from the corresponding cell by the cell types.
Successively, table 3 represents the sort of UEs that permit access
by the cell types.
TABLE-US-00002 TABLE 2 CSG cell General cell CSG indicator
Indicating `CSG cell` Indicating `Non-CSG cell` or not transmitted
CSG identity Transmitting supported Not transmitted CSG
identity
TABLE-US-00003 TABLE 3 CSG cell General cell UE not supporting CSG
Inaccessible Accessible Non-CSG member UE Inaccessible Accessible
Member CSG UE Accessible Accessible
In some frequency, the CSG cell and the (normal) macro cell may be
operated at the same time. Hereinafter, such frequency is called a
mixed carrier frequency. Network may reserve specific physical
layer cell indicators for the use of the CSG cell in the mixed
carrier frequency. The physical layer cell indicator is called a
physical cell identity (PCI) in the E-UTRAN system and is called a
physical scrambling code (PSC) in the UTRAN. For the convenience of
description, the physical layer cell indicator will be represented
as the PCI. In the mixed carrier frequency, the CSG cell notifies
the information of the PCIs reserved for the use of the CSG in the
current frequency via the system information. The UE that receives
the information may determine whether the cell is the CSG cell or
not from the PCI of the cell, when it finds a certain cell in the
corresponding frequency.
The UE that does not support the function related the CSG or does
not have the CSG list to which it belongs as a member is not
necessary to regard the CSG cell as the selectable cell in the
process of cell selection/reselection. In this case, the UE checks
only the PCI of the cell, and if the PCI is the PCI reserved as the
CSG, it may exclude the corresponding cell in the process of cell
selection/reselection. In general, the PCI of a certain cell may be
directly acknowledged by the UE in the process of checking the
presence of the corresponding cell existed in the physical
layer.
As for the UE that has the CGS list to which it belongs, when it
wants to know the list of the CSG cells nearby in the mixed carrier
frequency, it may know that the corresponding cell is the CSG cell
by finding the cell which has the PCI reserved as the use of the
CSG instead of checking the CSG indicators of the system
information for all cells found in the overall PCI range one by
one.
Hereinafter, the method of reselecting the cell related to the CGS
cell will be described.
The CSG cell is the cell to support a better service for the UE of
the corresponding CSG member. Accordingly, during the UE is camping
on the CSG cell, it may be not desirable to reselect the
inter-frequency cell in the aspect of the quality of service even
though the UE may detect the inter-frequency which has higher
frequency priority than that of serving frequency.
While the UE is camping on the CSG, in order to prevent
unconditionally reselecting the inter-frequency which has higher
frequency priority than that of the serving frequency, the UE
assumes that the frequency priority of the corresponding frequency
is higher than that of the other frequency in case that the CSG
cell of a certain frequency turns out to be the best ranked
according to the evaluation standard of cell reselection in the
frequency. Likewise, when the UE designates higher frequency
priority than the frequency priority that can be designated by the
network in a specific frequency by itself, the frequency priority
is referred to an implicit highest priority. By this, it may help
that the UE remains in the CSG cell with keeping the existing rule
of selecting the cell, the UE considers the frequency priority
first when the UE reselects the cell. If the UE in the CSG cell
reselects the non-CSG cell of the corresponding frequency, the UE
withdraws the assumption of the implicit highest priority for the
corresponding frequency, and use the frequency priority value
transferred by the network in evaluating the cell reselection. In
case that the UE detects another CSG cell of best ranked in the
frequency which has the same frequency priority while the UE is
camping on the CSG cell, it depends on the implementation of the UE
whether the UE reselects the CSG cell or remains in the CSG cell
which the UE is camping on.
The handover method related to the CSG cell will now be
described.
The UE in the state of RRC connection executes the general
measurement and mobility process on the basis of the configuration
provided by the network. The UE is not requested to support the
manual selection of CSG IDs during being in the state of RRC
connection. The handover to the HNB/HeNB is supported by the UE and
follows the framework of the handover controlled by the network.
The handover to the HNB/HeNB has three differences from the general
handover process.
1. Proximity Estimation: In case that the UE is able to detect
whether the CSG with the CSG ID included in the CGS white list of
the UE or a hybrid cell is close through the autonomous search
procedure, the UE may provide a proximity indication to the source
eNB. The proximity indication may be used as below: If there is no
measurement configuration of the frequency/RAT considered, it may
be configured that the source eNB orders the UE to execute
measurement and report of the considered frequency/RAT. The source
eNB may determine whether another action related to the handover to
the HNB/HeNB is executed on the basis of the proximity indication
received (For example, the source eNB may not be configured for the
UE to acquire the system information of the HNB/HeNB, if the
proximity indication is not received.).
2. PSC/PCI confusion: Since the typical cell size of the HNB/HeNB
is much smaller than that of the macro cell, the multiple HNB/HeNB
which have the identical PSC/PCI in the coverage of the source eNB
may exist. This may result in the condition which is called the
PSC/PCI confusion, and this is the case of the source of eNB not
determining the proper target cell for the handover from the
PSC/PCI included in the measurement report from the UE. The PSC/PCI
confusion can be solved by the UE reporting the global cell ID
(GCI) of the target HNB/HeNB.
3. Access Control: If the target cell is the hybrid cell,
prioritizing the allocated resources may be performed on the basis
of the membership status of the UE. The access control may be
performed by two processes: First, the UE reports the membership
status on the basis of the CSG ID and the CSG white list of the UE
which is received from the target cell, and the network discerns
the state of report.
The mobility from the eNB/HeNB to the CSG/hybrid cell of the HeNB
occurs with being accompanied by the S1 handover process.
Hereinafter, the source cell may be either one of the eNB or the
HeNB. The process may be applied to all scenarios for which the CSG
ID is provided by the UE or by the source eNB.
FIG. 13 is a flow chart illustrating the handover process of the
CSG cell.
Referring to FIG. 13, the handover process of the CSG cell will be
described below.
Step 1. The source eNB configures the proximity indication control
to the UE. For this, the source eNB may transmit a reconfiguration
message to the UE. The reconfiguration message includes the
information for the configuration of the proximity indication.
Step 2. When the UE (on the basis of the autonomous search
procedure) detects that the UE is close to the cell which has the
CSG ID included in the CSG white list of the UE, the UE transmits
"Entering" proximity indication. The proximity indication includes
the RAT and frequency of the cell.
Step 3. If there is no measurement configuration for the
frequency/RAT considered, the source eNB sets up the proper
measurement configuration including the measurement gap on the UE
depending on its need the UE may perform the measurement for the
RAT and frequency reported. For this, the source eNB transmits a
reconfiguration message to the UE. The reconfiguration message may
include the information of the configuration for the
measurement.
Also, if the UE does not exist in the geographical area where the
cells that have the CSG ID included in the CSG white list of the UE
are located, the network may use the proximity indication in order
to minimize the request for the handover preparation information of
the CSG/hybrid cell by avoiding requesting such information.
Step 4. The UE transmits the measurement report that includes the
PCI (for example, occurred by the event A3 triggered).
Step 5. The source eNB sets up the UE in order to perform acquiring
the system information and reporting a specific PCI.
Step 6. The UE performs acquiring the system information using the
autonomous gap, for example, the UE may terminate receiving or
transmitting within the range limit defined by [TS 36.133] to
acquire the proper system information from the target HeNB.
Step 7. The UE transmits the measurement report that includes (E-)
CGI, TAI, CSG ID and "member/non-member" indications.
Step 8. The source eNB includes the target E-CGI and CSG ID in the
handover required message which is requested to send via the MME.
If the target is the hybrid cell, the cell access mode of the
target is included.
Step 9. The MME performs the UE access control onto the CSG cell
based on the received CSG ID which is in the handover message
requested above and the CSG subscription data stored for the UE. If
the access control process fails, the MME terminates the handover
process by answering by a handover preparation failure message. In
case of the cell access mode, the MME determines the CSG membership
status of the UE that handovers to the hybrid cell, and includes it
in the handover request message.
Step 10-11. The MME transmits the handover request message that
includes the target CSG ID received via the handover message
requested above to the target HeNB. If the target is the hybrid
cell, the CSG membership status may be included in the handover
request message.
Step 12. The target HeNB checks if the CSG ID received via the
handover request message matches with the broadcasted CSG ID of the
target cell, and allocates the appropriate resource if the process
of checking above is done. The priority determination of the UE may
be also applied to the case that the above UE is indicated as a
member by the state of the CSG membership.
Step 13-14. The target HeNB transmits the handover request
acknowledgement message to the MME through the HeNB GW if it is
existed.
Step 15. The MME transmits the handover command message to the
source eNB.
Step 16. The source eNB transmits the handover command (the RRC
connection reconfiguration message including the mobility control
information) to the UE.
Steps 1 to 9, 15 and 16 may be applied to an inter-RAT mobility
from LTE to the HNB.
After transmitting the proximity indication "Enter" (step 2), if
the UE determines that the cell having the CSG ID included in the
CSG white list of the UE is not near any more, the UE transmits the
proximity indication "leaving" to the source eNB above. After
receiving the indication, the source eNB may reconfigure the UE to
terminate the measurement of the RAT and frequency reported.
According to the process above, in case that the UE has never
visited to the HeNB, for example, the UE visits to the hybrid cell
for the first time, steps 2 and 3 may not be performed.
The PCI confusion may be solved through steps 5 to 7. The source
eNB acquires the system information and may request to report any
PCI, whatever it is, which is not limited to the PSC/PCI of the CSG
or hybrid cell.
The parameter scaling related to the mobility influences on the
mobility determination of the UE according to the state of the UE
mobility will be described below. In case that the UE fast moves
through cells, it may fall into the disable state of service since
the mobility to neighboring cells are not timely performed.
Accordingly, the mobility performance is improved by optimizing the
value of the parameter related to the mobility with the speed of
the UE according to the speed of the UE. As described above, by
determining the mobility status (performing the MSE) and scaling
the parameter related to the mobility determination according to
the mobility status of the UE determined by the UE, the mobility of
the UE may be more effectively supported.
The mobility state of the UE may be divided to the high mobility
state, the medium mobility state and the normal mobility state.
Each mobility state may be determined on the basis of the number of
the handover performed by the UE and/or the number of the cell
reselection performed.
The UE in the state of RRC_IDLE performs the cell reselection if
the cell reselection criteria are satisfied. If the number of the
cell reselection performed by the UE for the specific time interval
(T.sub.CRmax) exceeds the first threshold value
(N.sub.CR.sub._.sub.H), the mobility state of the UE satisfies the
condition of the high mobility state. Meanwhile, if the number of
the cell reselection performed by the UE for the specific time
interval (T.sub.CRmax) exceeds the second threshold value
(N.sub.CR.sub._.sub.M) and does not exceed the first threshold
value (N.sub.CR.sub._.sub.H), the mobility state of the UE
satisfies the condition of the medium mobility state. If the number
of the cell reselection performed by the UE for the specific time
interval (T.sub.CRmax) does not exceed the second threshold value
(N.sub.CR.sub._.sub.M), the mobility state of the UE satisfies the
condition of the normal mobility state. However, in case that the
UE continually performs the cell reselection between the two
identical cells, it may not be counted as the number of the cell
reselection performed.
If a specific condition is satisfied when measuring the neighboring
cell, the UE in the RRC_CONNECTED state reports the result of the
measurement and performs the handover. If the number of the
handover performed by the UE for the specific time interval exceeds
the first threshold value, the mobility state of the UE satisfies
the condition of the high mobility state. Meanwhile, if the number
of the handover performed by the UE for the specific time interval
exceeds the second threshold value and does not exceed the first
threshold value, the mobility state of the UE satisfies the
condition of the medium mobility state. If the number of the
handover performed by the UE for the specific time interval does
not exceed the second threshold value, the mobility state of the UE
satisfies the condition of the normal mobility state.
If the UE in the RRC_IDLE or RRC_CONNECTED state detects that the
above described condition of the mobility state is satisfied, it
may enter into the corresponding mobility state. Entering into the
corresponding mobility state might be the determination of the UE
that its mobility state is the corresponding mobility state.
However, if it is determined that both condition of the high
mobility state and of the normal mobility state are not satisfied
for a specific time interval, the UE may enter into the normal
mobility state.
The UE which detects the mobility state may perform scaling the
mobility parameter on the basis of the mobility state. The UE in
the RRC_IDLE state may perform scaling the Tselection parameter,
and the UE in the RRC_CONNECTED state may perform scaling the
TimeToTrigger parameter. The scaling may be implemented by
multiplying a specific scaling factor to the Tselection parameter
or the TimeToTrigger parameter. The scaling factor may be different
according to the mobility state of the UE. For example, the scaling
factor in the high mobility state may be smaller than the scaling
factor in the medium mobility state. The scaling may not be
performed in the medium mobility state. The scaling may be
performed by the network or the cell as well as by the UE, and the
information for this may be given to the UE.
First, the scaling applied to the Tselection parameter used for the
reselection of a cell by the UE in the RRC_IDLE state will be
described in detail.
1) In case of the normal mobility state (neither the medium nor the
high mobility state), scaling Tselection is not performed.
2) In case of the high mobility state Scaling is performed by
multiplying the scaling factor sf-high to the Tselection.sub.EUTRA
in the E-UTRAN. Scaling is performed by multiplying the scaling
factor sf-high to the Tselection.sub.UTRA in the UTRAN. Scaling is
performed by multiplying the scaling factor sf-high to the
Tselection.sub.GERA in the GERAN. Scaling is performed by
multiplying the scaling factor sf-high to the
Tselection.sub.CDMA.sub._.sub.HPRD in the CDMA2000 HRPD. Scaling is
performed by multiplying the scaling factor sf-high to the
Tselection.sub.CDMA.sub._.sub.1.times.RTT in the CDMA2000
1.times.RTT.
3) In case of the medium mobility state Scaling is performed by
multiplying the scaling factor sf-medium to the
Tselection.sub.EUTRA in the E-UTRAN. Scaling is performed by
multiplying the scaling factor sf-medium to the Tselection.sub.UTRA
in the UTRAN. Scaling is performed by multiplying the scaling
factor sf-medium to the Tselection.sub.GERA in the GERAN. Scaling
is performed by multiplying the scaling factor sf-medium to the
Tselection.sub.CDMA.sub._.sub.HPRD in the CDMA2000 HRPD. Scaling is
performed by multiplying the scaling factor sf-medium to the
Tselection.sub.CDMA.sub._.sub.1.times.RTT in the CDMA2000
1.times.RTT.
The information parameter (e.g., scaling factor) needed for scaling
the Tselection parameter by the UE in the RRC_IDLE state may be
provided for the UE with being included in the system information
which is broadcasted. The UE may perform scaling if the information
parameter for scaling is included in the system information.
Next, the scaling applied to the TimeToTrigger parameter used for
reporting the measurement and/or the handover by the UE in the
RRC_CONNECTED state will be described in detail.
1) In case of the normal mobility state (neither the medium nor the
high mobility state), scaling the TimeToTrigger is not
performed.
2) In case of the high mobility state Scaling is performed by
multiplying the scaling factor sf-high to the TimeToTrigger.
3) In case of the medium mobility state Scaling is performed by
multiplying the scaling factor sf-medium to the TimeToTrigger.
As described above, more proper mobility performance may be
executed by applying a different mobility parameter according to
the mobility state of the UE. For example, in case that the UE
moves fast, by performing scaling according to the high mobility
state through the evaluation of the mobility via the MSE, the UE
may perform the mobility faster based on the mobility parameter
which becomes smaller.
The evaluation of the mobility state and the scaling of the
mobility parameter may result in a problem in the aspect of
performing the mobility due to the actual move of the UE and
performing the inter-frequency mobility which is not related to the
actual move of the UE. This will be described below.
(1) The problem in the aspect of the actual move of the UE.
As the mobile communication technology develops, the number of
communication service subscribers increases, and a very large
number of UEs may exist in one macro cell coverage. In this case,
the UE is provided or is expected to be offered with service by the
macro cell, the traffic of the macro cell may be overloaded. The
communication service provider may want to offload the traffic of
the macro cell in order to provide more effective and better
service for the subscriber. For this, by installing relatively
small coverage cells in a specific location within a macro cell
which has wide coverage, the communication system may be
implemented which is to provide service for the UEs in the small
cell coverage from a small cell instead of the macro cell. Such
communication system may be called the heterogeneous network.
In the heterogeneous network, the femto cell and/or the pico cell
whose coverage is much smaller may coexist in the macro cell
coverage. The UE counts the number of moves whenever it moves into
the pico cell and/or the femto cell by the cell reselection or the
handover while it moving. Hereinafter, the number of moves counted
by the UE will be referred to the mobility counter. The mobility
counter is the number of the cell reselection performed by the UE
in the RRC_IDLE state and/or the number of the handover performed
by the UE in the RRC_CONNECTED state, which is the basis of
determining the mobility state by evaluating the mobility
state.
Meanwhile, since the coverage of the femto cell and/or the pico
cell in the heterogeneous network is relatively much smaller than
that of the macro cell, the UE may perform mobility more frequently
even in case that the UE actually does not move with fast speed. In
this case, the UE may determine that the UE itself is in the high
mobility state or in the medium mobility state by the MSE. That is
because the UE constantly increases the mobility count even in case
of the UE moving into the femto cell and/or the pico cell whose
coverage is small. The mobility state evaluating as above
corresponds to the result in which the actual mobility state of the
UE is not properly reflected.
(2) The problem in the aspect of the inter-frequency mobility.
The reason why the UE moves into the cell whose frequency is
different from that of the currently serving cell is due to the
lack of the coverage of the currently serving cell frequency, that
is, due to the UE getting out of the coverage serviced according to
the current frequency. Otherwise, it may be because that it is
configured by the network that the UE moves to different frequency
according to the network operation policy or for the load
balancing, even if the UE exists in the coverage of the
corresponding frequency.
What the UE gets out of the coverage of the current frequency and
moves into cells with other frequency may be assumed that the
mobility is done by the physical moves of the actual UE. In this
case, it may be determined that the mobility state evaluated by the
MSE properly reflects the mobility of the actual UE.
However, in case that the UE moves into the cell of different
frequency although it is not lack of the coverage of the current
frequency, it is highly probable that the mobility is not performed
by actual physical movement of the UE. This is because the
inter-frequency mobility may be performed according to the priority
assigned to the cell frequency rather than the quality of service
provided for the location of the UE/the UE. In this case, it may be
determined that the mobility state evaluated according to the MSE
is higher than the actual mobility state since the mobility counter
which corresponds to the number of mobility performed according to
the mobility performance is increased without actual movement of
the UE.
As an example of the inter-frequency mobility, the autonomous top
priority configuration of the member CSG cell or the multimedia
broadcast multicast service (MBMS) of the UE may be also related to
the MSE. When the UE finds the CSG cell to which it belongs as a
member, the UE sets up the priority of cell reselection to be top
priority with respect to the frequency of the corresponding CSG
cell. That is, the UE sets up the frequency of the corresponding
CSG cell to be higher than other frequency in the cell reselection
priority list received from the network. Accordingly, the priority
of the frequency in which the CSG cell exists is set up as the top
priority value which is different from the cell reselection
priority received from the network, and the priority of the other
frequencies remains as the existing priority.
Also, in case that the UE prefers receiving the MBMS service, and
in case that the UE is located in the region where the MBMS service
is provided, the UE configures the cell reselection priority of the
frequency in which the MBMS service is provided as to the top
priority. That is, in the cell reselection priority list received
from the wireless network, the UE sets up the priority of the
frequency in which the MBMS service is provided to be higher than
the priority of the other frequency. Accordingly, the priority of
the frequency related to the MBMS service is set up to be the top
priority value which is different from the cell reselection
priority received from the network, and the priority of the other
frequencies remains as the existing priority.
As described above, regarding the inter-frequency mobility to the
frequency in which the top priority is assigned by the UE, the
mobility state evaluated according to the MSE may be determined to
be higher than the actual mobility state by increasing the mobility
counter without actual moves.
Hereinafter, this will be described in more detail referring to
FIG. 14.
FIG. 14 is a drawing illustrating an example of the mobility
performed by the UE in the wireless communication system.
Referring to FIG. 14, the paths A, C and E correspond to the actual
moves of the UE. Among these, the paths A and E where the cell
reselection is performed or the handover is performed are the paths
of the mobility performed by the UE, which become the object of the
mobility counting.
Although the paths B and D are not what the UE actually moves in,
but what the inter-frequency cell reselection or the handover is
performed in. The paths B and D are the paths of the mobility
performed by the UE, which become the object of the mobility
counting.
According to the existing MSE, among the steps A to E, the mobility
counter is updated after the steps A, B, D and E. However, since
the step B and D are objects of the mobility counting, although it
does not correspond to the actual moves of the UE, the step B and D
may be the factor which results in an error when the UE detects the
actual mobility state by the UE.
In this case, the mobility counter of the UE may be determined as
the state of being unnecessarily high, which may result in the
problem that the mobility parameter such as Tselection or
TimeToTrigger is improperly scaled.
In order to solve the problem that may be occurred by the MSE
described above, the network may provide the MSE control
information that the UE may use for controlling the MSE. The MSE
control information may be broadcasted from the network or directly
signaled to a specific UE.
The MSE control information may include the counting threshold
value and/or the prohibit timer.
When the UE updating the mobility counter value through performing
the mobility, the counting threshold value means the maximum value
of the mobility counter value that may be increased during the
prohibit timer is driving. In case that the counting threshold
value is effective, the UE is not able to update the mobility
counter as to the value exceeding the counting threshold value even
if the UE performs the mobility. The counting threshold value may
be included in the MSE control information with being configured as
a specific value. However, in case that the counting threshold
value is not included in the MSE control information, the UE may
assume that the counting threshold value is set to 1.
The prohibit timer value is the value to be set in the prohibit
timer that indicates the effective duration time of the counting
threshold value. When receiving the MSE control information, the UE
sets up the prohibit timer as to the prohibit timer value, and
start the prohibit timer. The UE does not terminate the prohibit
timer even in case of performing the mobility to another cell. Even
in case of performing the mobility to another cell which is
signaling the different prohibit timer value, the UE does not
terminate/discard the prohibit timer which is currently operating.
Instead, the UE sets up the prohibit timer to the newly signaled
prohibit timer value after the existing timer is terminated, and
let it start.
In case that the prohibit timer is in operating, that is, the
counting threshold is effective, the UE does not update the
mobility counter to the value exceeding the counting threshold
value even if the UE performs the mobility. Even if the UE performs
the mobility as many as the number of exceeding the counting
threshold value, the final mobility counter value is set to the
counting threshold value.
FIG. 15 is a flow chart illustrating the UE how to perform the MSE
according to an embodiment of the present invention.
Referring to FIG. 15, the UE receives the MSE control information
from the network (step, S1510). The MSE control information may
include the prohibit timer value and/or the counting threshold
value. If the counting threshold value is not included in the MSE
control information, the UE may assume that the counting threshold
value is 1.
The UE detects whether the prohibit timer is in operating (step,
S1520).
If the prohibit timer is not in operating, the UE set up the
prohibit timer to the prohibit timer value included in the MSE
control information received, and let it start (step, S1530a).
If the prohibit timer is in operating, the UE set up the prohibit
timer to the prohibit timer value included in the MSE control
information received above, and let it be started after the
prohibit timer is terminated (step, S1530b).
The UE performs the mobility if the mobility condition is satisfied
(S1540). If the cell reselection condition is satisfied, the UE in
the RRC idle state performs the cell reselection. The UE in the RRC
connected state performs the handover if the handover condition is
satisfied.
The UE determines whether the mobility counter is updated or not
after the mobility performed. The decision of updating includes
comparing the current mobility counter value with the counting
threshold value (N) received.
The UE updates the mobility counter if the mobility counter value
is smaller than the counting threshold value (step, S1560a).
Updating the mobility counter is to set up the value increased by 1
from the current mobility counter value as the new mobility counter
value.
If the mobility counter value is not smaller than the counting
threshold value, the UE does not update the mobility counter (step,
S1560b). That is, the UE may not update the mobility counter value
even though the mobility has been performed.
The UE performs the MSE on the basis of the mobility counter value
and scaling the mobility parameter (step, S1570).
Meanwhile, a plurality of prohibit timer values may be included in
the MSE information. Each of the prohibit timer values may be
related to the mobility state of the UE. For example, three
prohibit timer value may be provided to the three mobility state
(the high mobility, the medium mobility and the normal mobility).
In this case, the UE may set up the prohibit timer by selecting a
proper prohibit timer value according to its current mobility
state. Accordingly, only one prohibit timer may be operated for one
UE for a moment.
In the situation that the prohibit timer value is provided for the
UE according to the mobility state of the UE as above, in case that
the mobility state of the UE is changed while the prohibit timer is
in operating, the UE sets up the prohibit timer value to the
prohibit timer value that corresponds to the mobility state
changed, then let the prohibit timer which is set up start.
Meanwhile, the scaling factor values for scaling the prohibit timer
value according to the change of the mobility state of the UE may
be included in the MSE information. For example, if the prohibit
timer value which is applied in the general mobility state of the
UE is referred to as the basic prohibit timer, the prohibit timer
scaling factor for use of the medium mobility which is scaling the
basic prohibit timer may exist in case of the medium mobility
state, and the prohibit time scaling factor for use of the high
mobility which is scaling the basic prohibit timer may exist in
case of the high mobility state. The above scaling factors may be
implemented that the prohibit timer value is to be lowered when the
mobility state of the UE becomes high, and is to be increased when
the mobility state of the UE becomes low.
In the situation that the scaling factor that can be scaling the
prohibit timer is provided for the UE according to the change of
mobility state of the UE as above, if the mobility state of the UE
is changed while the prohibit timer is in operating, the UE sets up
the prohibit timer value as to that of being scaled after selecting
the scaling factor which is suitable for the change of the mobility
and scaling it. And then the UE may let the prohibit timer which is
set up start.
According to the embodiment of the present invention described with
referring to the drawings, more strengthen MSE may be provided
since the MSE control information is provided to the UE. According
to the embodiment of the present invention, in the heterogeneous
network where the macro cells and other small cells coexist, the
improper mobility counting due to the mobility performance which is
not related to the actual move of the UE may be prohibited.
According to an exemplary embodiment of the present invention, in
the wireless communication system in which inter-frequency mobility
is frequently caused, the improper mobility counting due to the
mobility performance which is not related to the actual move of the
UE may be prohibited. Through this, the mobility state of the UE
which is estimated by the MSE executed by the UE may more suitably
reflect the actual mobility of the UE. On the basis of this, the UE
may suitably execute mobility according to actual network
surroundings and the state of its mobility.
FIG. 16 is a block diagram that illustrates a wireless apparatus in
which the embodiment of the present invention can be implemented.
The apparatus may implement the operation of the UE according to
the embodiment described with referring to FIG. 15.
The wireless apparatus 1600 includes a processor 1610, a memory
1620 and a radio frequency (RF) unit 1630.
The processor 1610 implements the suggested function, process
and/or method. The processor 1610 may be configured to receive the
MSE control information and to determine whether the mobility
counter is updated. The processor 1610 may be configured to
determine whether the prohibit timer is operated on the basis of
the MSE control information. The processor 1610 is configured to
perform the MSE and to perform scaling the mobility parameter
according the mobility state estimated. The embodiment as described
above with referring to FIG. 15 may be implemented by the processor
1610 and the memory 1620.
The RF unit 1630 transmits and receives the wireless signal with
being connected to the processor 1610.
The processor 1610 may include an application specific integrated
circuit (ASIC), other chipsets, a logic circuit and/or a data
processing device. The memory 1620 may include a read-only memory
(ROM), a random access memory (RAM), a flash memory, a memory card,
a storing medium and/or other storing device. When an embodiment is
implemented by software, the above-described technique may be
implemented by the modules (a processing, a function, and the like)
that perform the aforementioned functions. The modules are stored
in the memory 1620, and may be executed by the processor 1610. The
memory 1620 may be included in or outside the processor 1610, and
may be functionally connected with the processor 1610 by various
known means.
Although the methods are described based on the flow charts as a
series of steps or blocks in the aforementioned exemplary system,
the present invention is not limited to the order of the steps. A
certain step may take place differently from the aforementioned
steps, with different order or at the same time. In addition, it
may be understood to one of ordinary skill in the art that the
steps shown in the flow chart are not exclusive, but rather may
include other steps, and one or more of the steps may be deleted
without influencing the scope of the present invention.
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